Method for producing a membrane from a crosslinked polymer blend, and corresponding fuel cell

Abstract

The present invention relates to a polymer blend membrane comprising a bridged polymer which is produced by a selected process. The membrane of the invention displays a significantly improved fracture toughness (elongation at break/stress) combined with virtually unchanged other properties. The membranes of the invention are suitable for producing membrane-electrode units for fuel cells.

1. A membrane comprising a bridged polymer obtainable by a process comprising the following steps:
 A. preparing a solution comprising a basic polymer (polymer I) having at least one amino group per repeating unit and at least one bridging reagent and, in addition, at least one basic catalyst in at least one suitable solvent, 
 B. casting a film using the solution obtained from step A), 
 C. removing the solvent from step A), 
 D. carrying out the bridging reaction in the film obtained in step C), 
 E. doping the film obtained in step D) with a strong acid, wherein at least one further polymer based on a polysulfone (polymer II) in addition to the basic polymer (polymer I) is added in step A). 
 
     
     
       2. A membrane as claimed in  claim 1 , wherein the bridging reagent has at least two epoxide groups or isocyanate groups per molecule. 
     
     
       3. A membrane as claimed in  claim 1 , wherein the bridging reagent is at least one compound of the formula (II) and/or (III) 
       
         
           
           
               
               
           
         
       
       where R 1  is a hydrocarbon group having from 1 to 30 carbon atoms. 
     
     
       4. A membrane as claimed in  claim 3 , wherein R 1  is 
       
         
           
           
               
               
           
         
       
       where m, k and I are identical or different and are each an integer from 1 to 6, and n is an integer from 1 to 10. 
     
     
       5. A membrane as claimed in  claim 1 , wherein the bridging reagent contains at least three epoxide groups per molecule. 
     
     
       6. A membrane as claimed in  claim 5 , wherein the bridging reagent is the compound 
       
         
           
           
               
               
           
         
       
     
     
       7. A membrane as claimed in  claim 1 , wherein the bridging reagent is bisphenol A glycidyl ether [BPAGDE] and/or 1,4-butanediol diglycidyl ether. 
     
     
       8. A membrane as claimed in  claim 1 , wherein the solution prepared in step A) contains from 0.1 to 7 mol % of the bridging reagent per unit of the basic polymer. 
     
     
       9. A membrane as claimed in  claim 1 , wherein polybenzimidazoles, polyimidazoles, polyvinylimidazoles, polybenzobisimidazoles and copolymers thereof are used as basic polymer. 
     
     
       10. A membrane as claimed in  claim 9 , wherein polybenzimidazoles used have the formula: 
       
         
           
           
               
               
           
         
       
       where R is alkylene, perfluoralkylene or a substituent of one of the following formulae: 
       
         
           
           
               
               
           
         
       
       and each alkylene and perfuoroalkylene group R preferably has from 1 to 10 carbon atoms. 
     
     
       11. A membrane as claimed in  claim 9 , wherein polybenzobisimidazoles used have the formula 
       
         
           
           
               
               
           
         
       
       where R is as defined in  claim 10 . 
     
     
       12. A membrane as claimed in  claim 1 , wherein the further polymer based on a polysulfone (polymer II) comprises one or more polysulfones comprising recurring units which have linking sulfone groups and correspond to the formulae 2A, 2B, 2C, 2D, 2E, 2F and/or 2G: 
       
         
           
           
               
               
           
         
       
       where the radicals R are identical or different and are each, independently of one another, 1,2-phenylene, 1,3-phenylene, 1,4-phenylene, 4,4′-biphenyl, a divalent radical of a heteroaromatic, a divalent radical of a C10-aromatic and/or a divalent radical of a C14-aromatic, where the polysulfone preferably has no sulfonic acid groups. 
     
     
       13. A membrane as claimed in  claim 12 , wherein the number average molecular weight of the polysulfone is greater than 30,000 g/mol. 
     
     
       14. A membrane as claimed in  claim 1 , wherein the solution prepared in step A) comprises from 1 to 99 percent by weight of the basic polymer, with the bridging reagent and the basic catalyst being included, and from 99 to 1 percent by weight of the polymer based on polysulfone. 
     
     
       15. A membrane as claimed in  claim 1 , wherein bridging in step D) is carried out by heating, so that bridging (step D) and drying (step C) are carried out simultaneously in one step. 
     
     
       16. A membrane as claimed in  claim 1 , wherein drying of the film is carried out at a temperature below the reaction temperature of the bridging reagent and the film is subsequently heated further for the purpose of bridging. 
     
     
       17. A membrane as claimed in  claim 1 , wherein bridging in step D) is carried out by irradiation with electromagnetic waves (photochemical reaction). 
     
     
       18. A membrane as claimed in  claim 1 , wherein the strong acid used in step E) is phosphoric acid and/or sulfuric acid. 
     
     
       19. A membrane as claimed in  claim 1 , wherein the treatment in step E) is carried out using water or an aqueous acid and the polysulfone bears sulfonic acid groups and/or protonated sulfonic acid groups. 
     
     
       20. A membrane as claimed in  claim 1 , wherein basic catalysts used are basic oxides and hydroxides of the elements of main groups I, II and III of the Periodic Table, hybrides of the elements of main group I of the Periodic Table and organolithium compounds. 
     
     
       21. A membrane as claimed in  claim 20 , wherein basic catalysts used are KOH, LiOH, NaOH, RbOH, CsOH, Ca(OH) 2 , Mg(OH) 2 , Ba(OH) 2 , LiH, NaH, KH, methyllithium and/or butyllithium. 
     
     
       22. A membrane as claimed in  claim 1 , wherein the basic catalyst is added to the solution in step A) in amounts of from 0.01 to 5 mol %, based on the bridging reagent used. 
     
     
       23. A membrane as claimed in  claim 4 , wherein n is 1. 
     
     
       24. A membrane as claimed in  claim 10 , wherein R has from 1 to 6 carbon atoms.